that the Gli2 transcription factor is critical for expression of mammary stem cell niche signals.

Mammatrophic hormone response
requires stromal Gli2

Previous studies have shown that MaSCs respond
to the mammatrophic hormones estrogen and
GH (32, 33). MaSCs do not, however, express the
receptors for these hormones (34), indicating that
the mammatrophic hormone effect is indirect.

Mammary stroma is an important mediator of
hormone effects on MaSC activity (24), and we find
that expression of estrogen receptor and GH receptor is markedly reduced, from 7 and 14%,

respectively, to 2% of individual stromal cells in
Gli2DS mice (Fig. 6B). We therefore examined the

Gli2 dependence of hormone response in FACS-isolated Fsp1Cre-marked mammary stromal cells
and indeed found that stimulation with GH or
with estrogen revealed significantly impaired induction of their target genes Igf1 or Hgf, respectively,
in cells from Gli2DS as compared to Gli2WT mice
(2.88-fold reduction for Igf1 and 3.16-fold reduction for Hgf; Fig. 6, D and E), reflecting the
significant reduction in expression of receptors
for these hormones (fig. S7).

These defects in hormonal response of mam-mary stroma are reminiscent of the incompleteresponse of patients suffering from the disorderCPHD to hormonal supplementation. This supple-mentation is provided because multiple peptidicpituitary hormones and steroidal hormones in-duced by pituitary hormones are deficient as aresult of the congenital hypopituitarism associatedwith CPHD. Supplementation with GH rescuesheight defects in these patients (35, 36), but ab-normal breast development often is not improved,even with estrogen supplementation (5). Gli2DSmice produce normal levels of pituitary hormonessuch as GH and prolactin (Fig. 4, G and H), as Gli2expression in the pituitary is not affected (Fsp1Creand Gli2nLacZ expression in the pituitary do notZhao et al., Science 356, eaal3485 (2017) 21 April 2017 6 of 12